Sex steroids and the initiation of puberty in male African catfish (Clarias gariepinus)

The effects of sex steroids on spermatogenesis and testicular androgen secr etion were studied in juvenile (spermatogonia present in testes) African ca tfish. Fish were implanted with Silastic pellets containing 11-ketotestoste rone (KT), 11 beta-hydroxyandrostenedione (OHA), androstenetrione (OA), and rostenedione (A), testosterone (T), 5 alpha-dihydrotestosterone (DHT), or e stradiol-17 beta (E-2) Control groups received steroid-free pellets. Two we eks later, testis tissue fragments were incubated with African catfish lute inizing hormone (LH) and the amount of OHA secreted in vitro (the main andr ogen produced by African catfish testes) was quantified. Tissue fragments w ere then fixed for histological analysis of spermatogenesis. Treatment with KT, OHA, and OA stimulated testicular growth and spermatogenesis (spermato cytes and spermatids were found), whereas T, DHT, A, or E-2 had no such eff ects. All steroids, except for DHT and E-2, reduced OHA secretion in the ab sence and presence of LH to similar to 10% of the control values. Previous studies have shown that KT, OHA, and OA have little effect on circulating L H levels in juvenile male African catfish, so that these androgens probably had direct effects on the testis. Inasmuch as OHA, OA, and KT have largely similar effects and because Ol-IA and OA are converted to KT in vivo, we s uggest that KT is physiologically the most relevant androgen for the initia tion of spermatogenesis in African catfish.